The present invention relates to a process for post-treating an ilmenite ore subjected to a selective chlorination treatment wherein the ilmenite ore resulting from the chlorination furnace is separated from the unreacted ore (including the unreacted ore and partially reacted ore), solid carbonaceous materials and other impurities contained therein thereby to obtain an artificial rutile with a TiO.sub.2 content of at least 95 % as a final product.
The term "ilmenite" herein used refers to common titaniferous iron ores having a wide range of compositions of titanium dioxide (hereinafter referred to as titanium oxide), and ferrous and ferric oxide.
A selective chlorination process for ilmenite ore is well known as a process for upgrading the ilmenite wherein the ilmenite ore is mixed with coke or other solid carbonaceous materials to form a mixture which is treated with chlorine gas to preferentially chlorinate the iron oxide contained in the ore, and titanium oxide is concentrated into the residue. Basically, the reaction control of this selective chlorination process depends on the preferential reaction between the iron oxide contained in the ilmenite ore and chlorine. There have been a number of patents on establishment of conditions such as the quantity of the solid carbonaceous material to be added, reaction temperature and the like, and regulation of these factors in order to stabilize such a selective reaction.
However, because chlorine reacts not only with the iron oxide contained in the ilmenite but also with the titanium oxide, the selective chlorination merely includes utilization of the relative difference in reactivity of chlorine with the iron oxide and the titanium oxide. As the chlorination reaction proceeds and the residual iron oxide reaches a certain limit value, chlorine begins to react with the titanium oxide, while the unreacted iron oxide remains intact.
Ordinarily, the chlorination furnace is operated in such a manner that the unreacted iron oxide exceeding the limit level is allowed to remain thereby to prevent the formation of titanium tetrachloride. Therefore, the ore discharging from the chlorination furnace contains the unreacted ore corresponding to the unreacted iron oxide or the partially reacted ore, and excessive solid carbonaceous materials which were not used for the chlorination reaction is discharged together therewith from the furnace. The mixed ore is too low in titanium value to use as a product. That is, in order to provide an artificial rutile having a TiO.sub.2 content of at least 95%, separation of the unreacted ore and excessive solid carbonaceous material from the substantially completed reacted ore must be carried out.
In Japanese Laid-Open Publication No. 2657/71, a process for post-treating ilmenite ore removed from a chlorination furnace is disclosed which comprises carrying out the separation of the unreacted ore by magnetic separation. Also, Japanese Laid-Open Publication No. 4319/73 discloses a treating process including a combination of a magnetic separation process and a tabling process for separating coke and silica. On the other hand, Japanese Laid-Open Publication No. 33906/72 proposes separation of silica and alumina by subjecting the titanium concentrate resulting from the chlorination furnace to an electrostatic separator and separation of excessive coke by floatation or an electrostatic separation.
However, in the method described in Japanese Laid-Open Publication No. 2657/71, it is necessary to cool the ore from the chlorination furnace in a reducing atmosphere such as carbon monoxide or methane so that the iron contained in the ore is maintained at or converted to FeO or Fe.sub.3 O.sub.4, thereby magnetizing the remaining iron, and to maintain the remaining iron contained in the recovered ore from the furnace at a level of at least 5%, and preferably at least 10%, for example, 12% in order to prevent the formation of titanium tetrachloride. Therefore, when such an ore from the furnace is subjected to a magnetic separation, the separated ore inevitably contains a larger portion of magnetic materials. As a consequence, the combination of heat loss due to the recycling of the magnetic portion to the chlorination furnace and high temperature required to vaporize ferrous chloride having a high boiling point introduced from lower iron oxides make the maintenance of the chlorination furnace at the reaction temperature difficult.
Further, since the coke has a wide range of a particle size due to its consumption attendant on the chlorination reaction and a portion thereof always exhibits the same physical behavior as the ore when being subjected to a tabling or electrostatic separation, a complete separation thereof is impossible. The separation of coke by flotation ordinarily involves the use of a collector of hydrocarbon type such as kerosene. Since the coke subjected to the chlorination reaction has adsorbed various materials in the course of the treatment and the quantity of the materials absorbed varies with the reaction conditions, it is necessary to determine each flotation condition according to the influence of the adsorbing action of the coke, which is not necessarily easy, and the separation is thus unsatisfactory.